The high viscosity of polyamidoamine epoxy hardeners requires the use of a viscosity reducing additive to lower the curative viscosity and permit more convenient processing. The need for a reactive diluent for high viscosity epoxy curatives is primarily the result of new and anticipated government regulations for environmentally safe products and lower emissions.
Thus, the epoxy industry is in need of a reactive diluent for fatty polyamidoamine hardeners which will reduce viscosity, minimizing or eliminating the use of materials which contribute to volatile organic content (VOC) level in an epoxy coating formulation. Materials which contribute to VOCs are primarily non-reactive solvents. They are currently used to obtain the appropriate formulation viscosity for paint and coating applications.
Viscosity reducing additives have involved the addition of (1) lower viscosity polyethyleneamines such as triethylenetetramine (TETA) or amidoamines (the reaction product polyethyleneamines and monobasic fatty acids), or (2) a non-reactive plasticizer such as phthalate esters or benzyl alcohol, and/or non-reactive diluent such as tertiary amines, aromatic hydrocarbons or alcohols. The viscosity of the entire epoxy formulation is sometimes reduced by adding aliphatic glycidyl ethers, hydrocarbon resins or acrylates to the resin side. Such additives are used to reduce the viscosity of the hardener or resin, and the entire epoxy formulation but at the cost of dry time, and/or at the cost of UV stability, and typically at higher system cost.
Belgian Patent 663,324 (1965) describes the synthesis of 1-aminoalkyl-2-alkyl-2-imidazoline by the reaction of nitriles and polyamines at elevated temperature under pressure. According to the patent the products are suitable as polyepoxy hardeners. However, in contrast, the CA abstract (CA 65-5465d) states the products are plasticizers for polyepoxides.